Slip screen structure for dry-type developing machines



June 24, 1958 F. o. TRUMP 2,839,978 \SLIP SCREEN STRUCTURE FOR DRY-TYPE DEVELOPING MACHINES Filed May 18, 1954 INVENTOR FREDERICK O- TRUMP av 15 740a? AT OQNEYS United St SLIP SCREEN STRUCTURE FOR DRY-TYPE DEVELOPENG MACHINES Application May 18, 1954, Serial No. 430,591

4 Claims. (CI. 95-94) This invention relates to a slip screen structure for use with apparatus for the developing and printing of sensitized sheet material through exposure to the gases of amrnonia and the like. Machines of this general type are commonly known in the trade as dry type white-print developing machines and are adapted to develop certain sensitized sheets or layers of material, as paper sheets coated with di'azo type compounds, by conducting the same through an area in which vapors, as ammonia vapors, are confined so as to expose the sensitized material to the action of the vapors.

Machines of the general type in which this invention is designed to provide marl-ted and extraordinary improvements in operation and efiiciency include a tank structure in which developing vapors are generated, one wall of the tank. being formed to provide for the passage of a sensitized sheet across the same for exposure in the developing zone. The sensitized sheet is commonly advanced by means of a moving endless sealing sleeve or flexible blanket, along one run of which the blanket hugs the wall for the purpose of frictionally moving the sensitized sheet through the developing zone and in order to prevent insofar as possible the escape of vapors from the chamber of the tank.

Conventional developing tanks of this character are commonly formed with a perforated wall of metal such as stainless steel or wire screening through the openings of which the vapors are passed and across which the sealing blanket is conveyed, or a wall opening having a series of closely spaced rollers to provide a frictionless surface against which the blanket can convey a sensitized sheet.

In the operation of the above and other specific types of such tanks a major problem has been the accumulation of sensitizing material such as the diazo coating compounds or other emulsions on the surfaces of the elements over which the material 'being developed is advanced.

Objectionable limitations of the perforated stainless steel type of tank wall over which the blanket is run for advancing a sheet include the inability to successfully handle materials having an emulsion easily damaged by frictional contact with a metallic surface; a tendency to limitthe complete dififusion of the developing vapors for contacting the exposed surface of a sheet and resulting in an unevenly developed image as by m-ottling or blotching the same or producing an objectionable background pattern over the surface of the sheet; a tendency to collect deposits of the materials on the surface of the perforated 'wall thus clogging the holes through which the vapors are passed and causing the sheets being developed to be progressively mess'ier and poorly reproducing a desired image; and a tendency to crease the sheets being de veloped when the surface of the metallic wall loses its initial slippery character and the coeificient of friction approaches that of the sealing blanket sleeve. Various attempts have been made to overcome the objectionable characteristics of this type of tank. One such attempt maybe seen in Patent No. 2,515,144, of July 11, 1950, to

ice Patent 2,839,978 Patented June 24, 1958 Trump et al., in which a moving positively driven metallic flexible link belt is interposed between the perforated tank 'wall and the rubber compound sealing sleeve of the device. Not only is this construction of necessity relatively expensive to build, but also the movement thereof is critical in synchronizing the travel of the belts. Moreover, the placing of a moving flexible link belt between the blanket at the entrance and exit ends of the developing zone greatly increases the leakage. Not only does this cause extreme discomfort to an operator, but also the loss of developing vapors is extremely high. The consumption of the developing agent, such as ammonia, has been found to be about twice that of a tank not so equipped with a second positively driven belt.

'In the roller type tank, as will be recognized, single sheets of material may pass between the rollers of the machine and thus be directed to the interior of the tank. Elaborate attempts have been made in this type of tank without success to solve the problem of accumulation of tacky deposits at both ends and particularly at the exit end of the machine, and to lesser extent on the rollers themselves. in some instances small rollers have been mounted in staggered rows to enable the handling of single sheets. Insofar as i am aware, however, no satis factory solution has been oifered for eliminating the objectiona ble features of this and the other above described machines.

An object of this invention is to eliminate the need for complicated mechanism in an effort to improve the operation of such machines and to overcome the objectionable features of prior art apparatus of the type described. Solution of this problem has become particularly important due to the growing use of diazo sensitize-d materials which have a heavy dye load and a heat sensitive base such as acetate film and other thermoplastics.

The invention resides in providing a perforated sheet or layer of a fluorocarbon material, more particularly polytetrafiuoroethylene, as a liner or screen material over which the material being developed may be advanced by the moving sleeve belt normally made of rubber com- .pounds, It has been found that use of this material as a liner as hereinafter set forth overcomes the shortcomings of the prior art devices as set forth above as well as contributing to an improved operation thereof. It has also been found possible to rearrange the construction of the tank opening to provide certain advantages, as will be more particularly pointed out herein.

The many advantages; and objects of the invention will be discussed. in connection with the accompanying drawings in which,

Fig. 1 is a greatly magnified view of a fragment of a liner sheet of this invention;

Fig. 2 is a schematic sectional view of a preferred form of developing tank in which the new sheet is utilized;

Fig. 3 is a similar view showing a liner sheet as mounted in a conventional perforated wall type of tank;

Fig. 4 is a similar view showing a liner sheet mounted in a conventional roller type of tank; and

Figs. 5, 6 and 7 are fragmentary detail views of modified arrangements for providing a liner or sheet of polytetrafluoroethylene material to accomplish the objects of the invention.

Referring to Fig. l a fragment of a liner sheet 1 of polytetrafiuoroethylene is shown having a series of perforated holes 2 therein. The holes 2 are shown as arranged in rows. They may equally as well if preferred be arranged in staggered relation as are the holes 3 shown in the metal wall structure 4 of Fig. 6.

The showing in the drawing of Fig. 1 is on a greatly enlarged scale. For dimensions of the sheet it has been found that the polytetrailuoroethylene material may be on the order of .010 of an inch in thickness and the holes may be of an extremely small diameter and closely ".031 of an inch. With a closely perforated material of this construction it has been found that the developing vapors are afforded a completely diffused effect over the .surface of the developing material and that a close perforation of the above specifications appears to permit the passage of vapors through the holes to form a halo effect spreading outwardly of each hole and intersecting the halo of adjacent holes to produce a complete diffusion of vapors. The noticeable result on the developed material is a total absence of any patterning effect in the background of the printed surface. Thus the holes 2 of the material need not be staggered in the effort to achieve greater diffusion of vapors.

The polytetrafluoroethylene material is chemically inert to developing vapors, is heat resistant, extremely slippery, and self-lubricating. The smooth slippery surface of the sheet 1 may be initially burnished, as by a steel roller if desired, before installing it in a tank assembly. It has been discovered, however, that continued use improves its frictionless qualities, so that in operation a continuous self-lubricating and polishing action is introduced to reduce the co-efficient of friction. A mirror-like surface is ultimately obtained and with no observable reduction in the thickness of material. The permanently waxy and non-adhesive qualities of this material thus prevent any accumulation of tacky substances through continued use.

It has also been found that the polytetrafluoroethylene material is not affected in any way by the temperatures at which the developing tanks may be operated. Accordingly this material may be used at all temperatures, at all speeds of travel for different degrees of development without causing any adverse effect on the most delicate of emulsions. Thus specialty materials can be fed into the developing zone at such temperatures and ammonia feed as to produce optimum conditions; and such optimum conditions may often mean development at one pass through the machine.

In applying the liner sheet of this invention to a developing tank, the material may be simply attached at the entrance end of the developing zone and left free and unattached at the exit end. The type of assembly illustrated by Fig. 2 shows a tank 5 provided with a downwardly facing opening indicated at 6 having entrance and exit flanges at 7 against which an endless sealing sleeve 8 is flexed to convey the sensitized layer past the open wall. At It) and ill, respectively, a conventional supply tube and heated vapor trough is indicated. As'shown by Fig. 2 the polytetrafluoroethylene material (sheet 1) is interposed between the sleeve bearing a sensitized sheet material as the single sheet 12 and the opening 6 and the flanged entrance and exit walls thereof. At 13 is indicated suitable means for releasably anchoring the entrance edge of the flexible sheet 1 adjacent the wall of the tank.

In Fig. 3 a polytetrafiuoroethylene sheet 1 of this invention is shown incorporated in a conventional tank of the type in which a perforated stainless steel wall 14 is formed to create a developing zone for sensitized materials. According to conventional practice the holes in this type of metallic wall 14 are staggered as indicated by Fig. 6 in the efiort to increase the diffusion of vapors. It should be noted that such tank perforations are on the order of .1875 of an inch in diameter and the spacing between holes of .250 of an inch. The diameter and spacing of the tank wall holes is dictated as a practical matter by the necessity of insuring a passage for vapors from the interior of the tank. The passing of sensitized sheets over the surface of the metal wall, as before stated, leaves a deposit of material which becomes tacky and accumulates sufficiently to close off the holes in a relatively short period of operation. An-

other factor tending to close the holes in this prior type of tank is the common practice of treating the sleeve with belt conditioners which rub off on the metal when the sleeve is run without a developing sheet as the sheet 12. The polytetrafluoroethylene sheet 1 applied as shown entirely eliminates any formation of tacky deposits. The sheet 1 in the tank of Fig. 3 is shown as affixed at the entrance end by a simple retaining strap 16 and may if preferred be likewise attached at the exit end.

In Fig. 4 the sheet 1 of this invention is indicated as applied. to a roller type of developing tank in which a series of rollers 17 extend across the open wall transversely of the path of the sleeve 18. In this construction the polytetrafluoroethylene sheet is laid over the entrance and exit ends of the wall and over the roller surfaces. The roller surfaces in effect are converted to function as a back up means for supporting the new sheet 1 which provides in this case an almost frictionless surface at the entrance and exit and also between these areas.

In Fig. 6 the fragmentary perforated wall 4 represents a wall similar to the wall 14 of Fig. 3 and over the outer surface of which a liquid dispersion of polytetrafluoroethylene may be sprayed to coat the wall. The coating of polytetrafluoroethylene indicated at 19 may be sprayed in successive layers of approximately one thousandth inch in thickness, each successive layer being fused or baked to build up a coating of the thickness desired. Improved results may be obtained due to the tendency of the coating to repel any deposit of chemical emulsions from the material being developed. The diffusion of vapors is not as g eat as in the case of the perforated sheet 1 but if a permanent lubricating wall is desired over a tank wall surface the coating may be added to a wall as that of Fig. 3 by spraying.

In Fig. 5 a woven sheet 25 of glass fibers is shown over the surfaces of which the coating of polytetrafiuoroethylene material as indicated at 26, has been placed as by spraying the same. In the sheet 25 holes 27 may be formed to permit the diffusion of developing vapors. Still another modification is shown by Fig. 7. This form consists of a loosely woven sheet 28 formed by threads of the polytetrafluoroethylene material itself. In this form the developing vapors are diffused through the interstices of the woven material for the development of the sensitized material and by reason of the loose weave no perforating is necessary.

The non-sticking, self-lubricating heat and chemical resistant properties of the polytetrafluoroethylene material in any of the above forms thus render the perforated liner sheet or sprayed coating as described an ideal surface over which to slide sensitized materials at high temperatures without sticking. Where prior apparatus has remained continuously in service over only relatively short periods of time, before cleaning of parts is required, it has been found that a liner sheet of this invention makes it possible to operate a machine indefinitely.

Among the advantages in addition to those hereinabove mentioned andattributable to the use of a liner sheet of the type disclosed herein are: the elimination of a tendency of the vapors to form condensation which might cause spots on the sensitized material; the elimination of noise, as a rumbling, caused by a sealing sleeve traveling over a perforated surface (Fig. 3) or rollers (Fig. 4) as is frequently the case when no developing pass is taking place; the increase in the life of sealing sleeves due to the permanent lubrication and resulting reduction in friction; the elimination of shut-down periods for cleansing the tank and applying various belt conditioners; the reduction of power requirements and strain on the driving mechanism of the sleeve; the easier tracking of sensitized material when fed into the machine on a continuous web; the elimination of creasing in large sheets; the elimination down the machine; and the elimination of elaborate and 5 relatively complicated mechanism to reduce friction with a saving in consumption of the vapor generating substances.

The preferred manner of applying a sheet 1 to a tank is shown by Fig. 2. In the tank of Fig. 2 the free end of the sheet is fed over the opening 6 by movement of the sleeve 8. The entrance end edge thereof is folded over and held in clamped engagement by the inner folded edge 20 of a metal holder plate 21. The plate 21 at its outer edge is provided with hook members 22 which are removably hooked over a bracket 23 suitably fixed on the tank structure adjacent the entrance end of the sleeve path. Thus an operator can unhook the sheet 1, with draw it for inspection or other purposes and easily reinsert the same or a replacement sheet.

What is claimed is:

1. In a dry-type developing apparatus, having a perforated developing tank, a sealing sleeve embracing said tank and movable to advance exposed sensitized material from an infeed portion of said tank to an outfeed portion thereof; a foraminous slip screen interposed between said tank and said sleeve, said slip screen being surfaced with a material having the anti-friction characteristics of polytetralluoroethylene, one end of said slip screen being removably secured at the infeed portion of said tank and the opposite end of said slip screen extending in free floating fashion beyond the outfeed portion of said tank.

2. Apparatus as in claim 1, wherein the slip screen is a solid perforated sheet of polytetrafluoroethylene having a smooth and regular contour interrupted only by the perforations.

3. Apparatus as in claim 2 wherein the sheet has a thickness in the order of .010" and the perforations have a diameter of about .020 and are spaced apart about .030.

4. In a dry-type developing apparatus, having a perforated developing tank, a sealing sleeve embracing said tank and movable to advance exposed sensitized material along the perforated tank to expose same to developing vapors; a slip screen interposed between said tank and said sleeve, said slip screen being formed of an integral sheet of polytetrafiuoroethylene and said sheet having perforations therein of a diameter of about .202, said perforations being spaced apart about .030" and said sheet having a thickness in the order of .010, the surface of said slip screen continguous with said sleeve being of smooth and regular contour except as interrupted by said perforations whereby the developing vapors in said tank are etfectively sealed 01f by said sleeve as it moves therealong in the absence of sensitized material therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 2,515,144 Trump et al July 11, 1950 FOREIGN PATENTS 598,921 Great Britain Mar. 1, 1948 OTHER REFERENCES The Rubber and Plastic Age, volume XXXV, No. 6, June 1954, pages 278 and 279.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Frederick 06 Trump Patent Noo 2,839,978 June 24, 1958 It is hereby certified that error appears in the"; printedspecification of the above numbered patent requiring correction andthat the saiai Letters Patent should read as corrected below,

Column 6, line 12, for "202"" read ,O2O

Signed and sealed this 26th day 'of August 1958.,

ROBERT C WATSON Attesting Officer Comnissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,839,978 June 24, 1958 i Frederick O, Trump It is hereby certified that error appears in the printedxspecif-ication of the aboxTe num bered patent requiring correction and that the said Letters Patent should read as corrected below,

Column 6, line 12, for "$20? read 020" Signed and sealed this 26th day? of August 1958.,

(SEAL) KARL H, AXLINE ROBERT C. WATSON Attesting Officer Comnissioner of Patents 

